In typical commercial or industrial laundry processes, textile materials such as sheets, towels, wipes, garments, tablecloths, etc. are commonly laundered at elevated temperatures with alkaline detergent materials. Such detergent materials typically contain a source of alkalinity such as an alkali metal hydroxide, alkali metal silicate, alkali metal carbonate or other such base component. When the linen is treated with an alkaline detergent composition a certain amount of carryover alkalinity may occur. Carryover alkalinity refers to the chemistry that is contained within the linen (that has not been completely removed) that is available for the next step. For example, when the detergent use solution provides an alkaline environment, it is expected that the detergent use solution will provide a certain amount of carryover alkalinity for a subsequent sour treatment step unless all of the detergent use solution is removed by rinsing. The residual components of the alkaline detergents remaining in or on the laundered item can result in fabric damage and skin irritation by the wearer of the washed fabric. This is particularly a problem with towels, sheets and garments. Sour materials contain acid components that neutralize alkaline residues on the fabric.
Another challenge in laundry processes are iron and other metals. Such contaminants may be present due to stains, such as rust, or present due to water utilized within the laundry process, such as transition metals resulting from inputted water sources and/or steam to heat a laundry process. Iron can enter the water at the source or be picked up from corroding (or lines in various states of corrosion) water lines and tanks. Iron may be present in water sources in a soluble colorless form called ferrous iron. When exposed to air, ferrous iron rapidly converts to insoluble ferric iron, which can vary in color from yellow to reddish brown. If not properly removed, iron and other metals can cause permanent yellowing of fabrics and loss of fabric life due to tensile strength loss. Metal content can further result in detergent inactivation and/or inhibition, accelerated loss of oxidizing chemistries used in a laundry process, shading due to deposition of metals, as well as shading due to optical brightener modification, and still other detrimental laundry effects.
To date the primary approach to removing metals from water sources utilized in laundry processes focus on water softening equipment to reduce iron impurities. In addition, the approach to remove metals from stains to date has primarily relied upon the use of high levels of caustic, which can damage delicate fabrics and, if not properly removed and brought back to neutral pH, can result in exposure of the caustic to human skin. Current laundry sour compositions to help remove residual alkali and for iron control generally include strong acids such as fluoroacetic acid, phosphoric acid, hydrofluoric acid, and hexafluorosilicic acid which are environmentally undesirable and/or hazardous.
As can be seen, there is a continuing need in the art for the development of iron and other metal control treatments after alkaline washing that not only prevent yellow staining of laundered fabrics, and remove residual caustic, but also that are environmentally friendly and sustainable. Moreover, formulations for laundry applications present distinct challenges in comparison to warewash or other hard surface cleaning applications where water conditioning and metal control may also be required. Laundry presents unique challenges of a greater surface area (relative to warewashing or hard surface) and requiring chelants to treat both hardness ions and transition metals (iron, copper, manganese).
Moreover, the use of surfactants and/or chelants that are common in warewashing applications do not readily provide same benefits in laundry applications. This is primarily a result of the differences between the substrates being treated, namely porous textiles in laundry present distinct challenges from hard surfaces treated in warewashing applications. For example, a towel, such as a terry towel, will absorb or have contaminants deposited on the substrate and can be difficult to remove; unlike warewash substrates which may have a deposit on a surface only in the form of a film which is easier to remove with detergent compositions. The adsorption of inorganic ions on fibers and soil in laundry applications can even modify the surface charge of the solids and as a result either compete with or enhance the adsorption of surfactants to the surface. This presents additional difficulties in treating laundry substrates in comparison to warewash hard surfaces. It is an object to provide laundry compositions and methods which provide iron and other metal control and prevention of yellowing that prevent yellowing at least as well as commercially available, less environmentally friendly sour treatment alternatives.
A further object is to provide a non-phosphorous laundry additive composition for the control of transition metals and beneficial laundry performance.
A further object is to provide methods and compositions for improving laundry quality in multiple areas including detergency, bleaching and wastewater operations.
Other objects, advantages and features of the present invention will become apparent from the following specification taken in conjunction with the accompanying drawings.